This disclosure relates generally to a liquid separator for removing a liquid from a sample of a breathing gas and an airway adapter.
When a patient is mechanically ventilated with a conventional ventilator, an endotracheal tube is placed into a trachea so that it goes through oral or nasal cavity and larynx. The other end of the endotracheal tube is connected to a breathing circuit Y-piece through a luer type connector. If the patient is gas monitored with a sidestream gas analyzer, an airway adapter used for sampling the breathing gas that is analyzed by the gas analyzer is normally connected between connectors of the endotracheal tube and the breathing circuit Y-piece. During an inspiration the fresh breathing gas including higher oxygen (O2) concentration flows into the patients lungs through an inspiratory limb of the breathing circuit Y-piece, the airway adapter, the endotracheal tube and their connectors, then to a trachea, a bronchus, a bronchi, bronchioles and finally reaching an alveoli deep in the lungs, where all the gas exchange actually occurs. Carbon dioxide (CO2) molecules in hemoglobin of a blood flowing in tiny blood vessels around the alveoli are replaced with O2 molecules in the fresh breathing gas through the thin walls of the alveoli. O2 molecules take their place in the hemoglobin, whereas CO2 molecules flow out from the patient within the used expired breathing gas, through the same path as the fresh gas came in during the inspiration. Thus a gas concentration of the breathing gas measured by the gas analyzer is somewhat proportional to the gas concentration in the blood. If anesthetic agents are used they flow in to the patient during inspiration and the content not adsorbed by the patient flows out from the patient during expiration, which can be monitored with a gas analyzer as well.
The conventional patient side part of the breathing circuit, which is also shown in FIG. 1, usually consists of an endotracheal tube 2 connected to a patient 1 and to a sidestream type airway adapter 3 used for sampling the breathing gas for the gas analyzing purposes and a Y-piece 4 that connects the patient side part of the breathing circuit to the ventilator 5 through breathing circuit tubing for inspiratory gas 6 and expiratory gas 7. The gas analyzer 8 is placed further away from the patient close to or into the host device such as the ventilator 5. The breathing gas sample withdrawn from the patient's breathing is sucked by the gas analyzer 8 from the airway adapter 3, through a sampling port 9, which in connection with the breathing gases, through a sampling tube 10 and through a water separation unit 11 into the gas analyzer 8 to be analyzed. The length of the sampling tube 10 may vary from 2 to 6 meters and the inner diameter of the tube may vary from 1.2 to 2 mm. The breathing gas includes close to 100% humidity, which condensates into water in the sampling tube 10. The breathing gas may also include other liquid substances such as blood, mucus etc. that may enter the sampling tube 10. The water separation unit 11 usually comprises a porous membrane or a similar structure that separates the water or liquid substance from the gas flowing in the tube 10, preventing it to enter the sensitive parts inside the analyzer.
The inner diameter and the length of the sampling tube together with the sampling gas flow speed mostly determine the total system response time and the total system rise time of the gas analyzer. The length of the tubing is normally determined by the use environment in the hospital and is between 2 to 6 meters. It would be beneficial to have high sampling gas flow speed to decrease the total system response and rise times, but the tendency is to have the sampling gas flow speed below 200 ml/min or advantageously approximately at 50 ml/min to enable the gas monitoring of small patients whose tidal volumes may be as low as 2 ml. The advantageous choice to decrease the total system response and rise times is to decrease the diameter of the sampling tube. However as the diameter is decreased the condensed water and other liquid substances block the sampling tube easily deteriorating the measurement system rise time and increasing the measurement system response time or even preventing the whole gas analyzing as the sample gas is not allowed to enter the gas analyzer.
Some prior art systems may comprise a cylindrical water separation unit located partially inside the airway adapter breathing flow path and the volume inside the sample gas tube, which is in connection with the airway adapter. Such systems generate high and unwanted flow resistance to the gas flow disturbing the gas exchange in the lungs. Such systems are also position sensitive and easily get blocked by the condensed water and other liquid substances in certain positions.